Preheat oven to 375˚F.
Grease a 9x13 baking dish with cooking spray and set aside.
Prepare pasta according to the directions on the package.
In the meantime, heat up olive oil in a 12-inch skillet set over medium-high heat.
Add diced onions to the hot oil and cook for 3 minutes.
Stir in garlic and cook for 15 seconds.
Add zucchini and mushrooms; season with salt and pepper, and cook for 5 minutes, or until just tender. Stir frequently.
Drain pasta and return it to the pot.
To the pasta, add the cooked vegetables, cream cheese, sour cream, pasta sauce, half of the mozzarella, and seasonings; mix and stir until everything is incorporated and cheeses are melted.
Taste mixture for salt and pepper, and adjust accordingly.
Pour mixture into previously prepared baking dish.
Top with remaining mozzarella cheese.
Bake for 22 to 25 minutes, or until bubbly, and cheese is completely melted.
Remove from oven and let stand 8 to 10 minutes.
Top with fresh parsley and serve.